Not sure if it could be something this simple, but I remember reading from Palmer's book, he mentions just taking care to not disturb the yeast layer on the bottom when pouring and gives a story about a guy pouring him a homebrew and sloshing around the bottle to get it all out (yeast). I always try to pour my home brews carefully out of my bottles and try to leave a little bit of beer on the bottom to not disturb the yeast layer and don't usually have an issue, ya know, besides the usual. Not sure if this is the issue, but just a suggestion.